Ynys Môn is a UK Parliamentary and Welsh Parliament constituency, covering the entire Island of Anglesey. The Parliamentary seat was first contested in 1536, long before the Welsh Parliament had even been thought about. The Welsh Parliament seat was first contested in 1999. Ynys Môn has a mixed political past, with Conservative, Labour and Plaid Cymru having returned strong results in Parliamentary and Assembly elections. The largest population centre is Holyhead.
Ynys Môn is coterminous with the Isle of Anglesey County Council local authority area. Following a reorganisation of authority in 2022, it is made up of the following electoral divisions: Parc a'r Mynydd, Tref Cybi, Ynys Gybi, Bro'r Llynnoedd, Talybolin, Twrcelyn, Crigyll, Cefni, Canolbarth Mon, Bro Aberffraw, Bodowyr, Aethwy, Seiriol, Lilgwy.